Various types of liner hanger have been proposed for hanging a liner from a casing string in a well. Many liner hangers are set with slips activated by the liner hanger running tool. Liner hangers with multiple parts pose a significant liability when one or more of the parts become loose in the well, thereby disrupting the setting operation and making retrieval difficult. Other liner hangers and running tools cannot perform conventional cementing operations through the running tool before setting the liner hanger in the well.
Conventional liner hangers have problems supporting heavy liners with the weight of one million pounds or more. Some liner hangers successfully support the liner weight, but do not reliably seal with the casing string. Other liner hangers are not able to obtain burst and/or collapse characteristics equal to that of the casing. A preferred liner hanger maintains a collapse and burst strength at least substantially equal to that of both the casing and the liner.
Another significant problem with some liner hangers is that the running tool cannot be reliably disengaged from the set liner hanger for retrieval to the surface. This problem with liner hangers becomes more involved with the desirability to rotate the liner with the work string in the well, e.g., for a liner drilling operation, wherein the operator desires to disengage the work string and tool when the liner hanger has been set, thereby allowing the running tool and the work string to be retrieved from the well.
Publication 2001/0020532A1 discloses a tool for hanging a liner by pipe expansion. U.S. Pat. No. 3,948,321 discloses a reinforcing swage which remains downhole when the tool is retrieved to the surface. U.S. Pat. No. 6,705,395 discloses a radially expanded liner hanger which uses an axially movable annular piston to expand a tubular member. U.S. Pat. Nos. 7,225,880 and 7,278,492 disclose an expandable liner hanger system and method.
The disadvantages of the prior art are overcome by the present invention, and an improved liner hanger system and method of releasing the liner hanger are hereinafter disclosed.